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The vapour pressure of water at 20 °C is 17 mm Hg. What is the vapour pressure of solution containing 2.8 g urea in 50 g of water?

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प्रश्न

The vapour pressure of water at 20°C is 17 mm Hg. What is the vapour pressure of solution containing 2.8 g urea in 50 g of water?

योग
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उत्तर

Given: Vapour pressure of pure water = `"P"_1^0` = 17 mm Hg

Mass of urea (W2) = 2.8 g

Mass of water (W1) = 50 g

To find: Vapour pressure of the solution (P1)

Formula: `(P_1^0 - P_1)/P_1^0 = (W_2M_1)/(M_2W_1)`

Calculation:

Molar mass of urea (NH2CONH2) = 14 + 2 + 12 + 16 + 14 + 2 = 60 g mol–1

Molar mass of water = 18 g mol–1

Now, using formula,

`(P_1^0 - P_1)/P_1^0 = (W_2M_1)/(M_2W_1)`

= `(17 "mm Hg – P"_1)/(17 "mm Hg") = (2.8 g xx 18 g  mol^-1)/(50 g xx 60 g  mol^-1)`

∴ `(17 "mm Hg – P"_1)/(17 "mm Hg") = 0.0168`

∴ 17 mm Hg – P1 = 0.0168 × 17 mm Hg

∴ 17 mm Hg – P1 = 0.2856 mm Hg

∴ P1 = 17 mm Hg – 0.2856 mm Hg = 16.71 mm Hg

Vapour pressure of the given solution is 16.71 mm Hg.

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अध्याय 2: Solutions - Exercises [पृष्ठ ४६]

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बालभारती Chemistry [English] Standard 12 Maharashtra State Board
अध्याय 2 Solutions
Exercises | Q 9 | पृष्ठ ४६

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